In currently conventional non-volatile data storage sub-systems, disks (or storage media having other geometries) are required to perform a significant number of tasks beyond the simple non-volatile storing and retrieving of data. For example, the health of the non-volatile storage medium should be frequently verified and recorded to insure the integrity of the data stored in a non-volatile manner on the medium. Tasks related to the health of the non-volatile storage medium are sometimes herein called “data integrity tasks” or “data integrity checks.” These data integrity checks can require a significant proportion of the non-volatile storage medium's capacity and/or a significant proportion of the non-volatile storage sub-system's bandwidth.
When a computer system, including a non-volatile storage sub-system, detects a loss of external power supply, the computer system conventionally goes into an emergency shutdown procedure. During this shutdown period, the system is conventionally powered by an Uninterruptible Power Supply (UPS) which can prolong the operation of the computer system life by a short period (usually a few minutes). During this period, certain data called a “write cache,” which is held in dynamic memory (that is, a form of volatile memory) on the host system, is “downloaded,” in due course, to the non-volatile storage medium of the non-volatile storage sub-system. However, applications operate on the assumption that a write operation is successful when the application's data is merely written to the write cache in the volatile memory. For this reason, if a power failure (that is, running out of UPS power) occurs before the download of the application's data from volatile memory to the non-volatile storage medium of the non-volatile storage sub-system, then it is highly likely that at least some application data (for example, online data) will be lost, which is, of course, a generally bad outcome.
As a terminology note, “non-volatile” herein refers to data storage where the maintaining of the saved data requires no power, or very, very little power. As will be appreciated by those of skill in the art, non-volatile storage sub-systems usually do require power (usually electrical power) to write data (or to overwrite data in non-volatile data storage sub-systems that allow for overwrite of data).